Integrated circuit on corrugated substrate

ABSTRACT

By forming MOSFETs on a substrate having pre-existing ridges of semiconductor material (i.e., a “corrugated substrate”), the resolution limitations associated with conventional semiconductor manufacturing processes can be overcome, and high-performance, low-power transistors can be reliably and repeatably produced. Forming a corrugated substrate prior to actual device formation allows the ridges on the corrugated substrate to be created using high precision techniques that are not ordinarily suitable for device production. MOSFETs that subsequently incorporate the high-precision ridges into their channel regions will typically exhibit much more precise and less variable performance than similar MOSFETs formed using optical lithography-based techniques that cannot provide the same degree of patterning accuracy. Additional performance enhancement techniques such as pulse-shaped doping and “wrapped” gates can be used in conjunction with the segmented channel regions to further enhance device performance.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/173,231, entitled “Integrated Circuit On Corrugated Substrate” filedJul. 1, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of semiconductor integrated-circuitdevices and manufacturing, and in particular to structures for enhancingminiature transistor manufacturability and performance.

2. Related Art

Semiconductor integrated-circuit (IC) manufacturers face growingchallenges to accurately and reliably produce ever-smaller transistorsin order to improve the cost and performance (speed and/orfunctionality) of modern electronic devices. The most basic buildingblock used in a digital IC device is the metal-oxide-semiconductor fieldeffect transistor (MOSFET). As MOSFETs are scaled below 100 nm inminimum lateral dimension (i.e., the minimum feature size such as thegate length is less than 100 nm), size-related performance andmanufacturing issues become increasingly significant.

For example, the short gate lengths in modern MOSFETs can result inrelatively large source-to-drain leakage currents. Such leakage currentscan cause ICs incorporating those MOSFETs to exhibit undesirably largestatic power consumption. Conventional efforts to suppresssource-to-drain leakage current typically involve increasing the netdopant concentration in the channel region (e.g., to a net dopantconcentration greater than 10¹⁸ atoms/cm³), increasing gate capacitance,and decreasing the depths of the source and drain junctions adjacent tothe channel. A high net dopant concentration in the channel regionserves to confine the drain-induced lateral electric field to the drainregion, and thereby minimizes the effect of drain bias on the electricpotential in the channel region near to the source. At the same time, byincreasing the capacitive coupling between the gate electrode and thechannel region (e.g., by decreasing the thickness of the gatedielectric), dominant control over the channel potential (i.e.,controlling whether the transistor is on or off) is maintained by thegate electrode rather than the drain, thereby allowing the gate-inducedelectric field to more effectively suppress source-to-drain leakagecurrent. By keeping the depths of the source and drain junctionsadjacent to the channel shallower than the length of the channel region,sub-surface leakage currents can be suppressed.

Unfortunately, decreasing the gate dielectric thickness leads toundesirable leakage between the gate electrode and channel region.Furthermore, carrier mobility in the small channel regions of modernMOSFETS can be significantly degraded by high dopant concentration,which results in lower “on-current” for the transistor. The parasiticseries resistance of the source and drain regions increases withdecreasing junction depth, which also results in lower on-current forthe transistor. Therefore, as steps are taken in modern MOSFET designsto reduce static power consumption (i.e., reduce source-to-drain leakagecurrent), overall transistor performance (i.e., on-current) can suffer.

Another problem associated with smaller MOSFET dimensions relates to thesensitivity of device performance to dimensional variation. For devicesformed using 180 nm technology generation (and below) processes,relatively small differences in, for example, gate length can result insignificant performance differences. However, the IC manufacturingprocesses used to create those devices (e.g., optical lithography) areunable to provide the device-to-device dimensional consistency requiredto render such performance differences negligible. Consequently, circuitdesigners must design for worst-case scenarios to accommodate the widerange of device performance levels, thereby sacrificing overall ICperformance to accommodate manufacturability concerns.

Accordingly, it is desirable to provide structures and methods thatallow high-performance, low-static-power, and low-variability sub-100 nmMOSFET production.

SUMMARY OF THE INVENTION

Conventional metal-oxide-semiconductor field effect transistor (MOSFET)designs face significant challenges as they are scaled down to improvecost and/or performance with each new generation of technology used tomanufacture integrated circuits (ICs). In particular, the techniquesused to reduce static power consumption by minimizing source-to-drainleakage current (e.g., increased channel doping, decreasedgate-dielectric thickness, and decreased source and drain junctiondepths) tend to also decrease transistor performance by decreasingon-current. By forming MOSFETs using a semiconductor substrate havingprecisely-formed and regularly-spaced stripes (ridges of semiconductormaterial(s)), both high performance (i.e., high on-current) and lowstatic power consumption (i.e., low source-to-drain leakage current) canbe achieved. The stripes enable the formation of segmented channelregions that accommodate a wide range of gate-electrode configurationoptions and also provide greater performance consistency betweendevices.

In one embodiment, a MOSFET can include a segmented channel region, inwhich one or more dimensionally precise ridge(s) of semiconductormaterial (or materials) connect the source and drain regions. The ridgescan themselves be formed on an elevated base region that extends apredetermined height above the adjacent substrate surfaces. Aninsulating material partially surrounds the ridge(s), so that a topportion (“tip”) of each ridge is exposed prior to the formation of thegate stack (i.e. the gate-dielectric and gate-electrode layers). A gateelectrode (and interposing gate-dielectric layer(s)) for each ridge isformed over the exposed tips of the ridges and “wraps” around those tipsto provide enhanced control over source-to-drain leakage currents. (Thegate electrode “straddles” the top portion of each ridge.) Heavily dopedsub-surface regions within the ridges that begin at or near to thebottom of the tip (corresponding to the level of the insulatingmaterial) serve to further reduce source-to-drain leakage currents,thereby minimizing the static power consumption of the transistor.According to various other embodiments, any on-current enhancement orleakage-current reduction techniques applicable to conventional MOSFETconstructions can also be applied.

In another embodiment, an IC (and method for producing the IC)incorporates multiple MOSFETs formed on pre-existing ridges on acorrugated substrate. Since the ridges on the corrugated substrate aregeometrically very simple and very regular, high-precision fabricationtechniques (e.g., imprint lithography or spacer lithography) can be usedthat would normally be impractical for actual device production. Oncethe corrugated substrate is available, the ridges on the substrate canbe patterned based on the desired functional regions for the IC (i.e.,by removing the ridges in the non-functional regions), and then formingan insulation layer around and between the functional regions. Gatedielectric layer(s) and gate electrodes can then be formed over theridges in the desired transistor locations, and various dopingoperations can be performed to define the source, drain, and channelregions for the MOSFETs. The IC formed in this manner will includeMOSFETs having channel regions formed by one or more of the ridges,which helps to ensure that the MOSFETs exhibit accurate and consistentperformance from device to device. Adjacent MOSFETs in the IC (in thedirection of the original ridges) can have precisely aligned channelregion semiconductor segments, because those segments were originallyformed from continuous ridges (i.e., the pre-existing ridges on thecorrugated substrate). In various embodiments, the MOSFETs can includevarious source-to-drain leakage current reduction techniques such asheavily doped sub-surface regions in channel regions and wrapped gates(i.e., gates that wrap around the top portions of the ridges in thechannel regions). In another embodiment, ridges in a pattern between twotransistor locations can be filled in with electrically conductivematerial to form an electrical interconnect between the two transistorlocations, thereby reducing metallization requirements.

A semiconductor wafer can include one or more sets of precisely formedridges, with each set of ridges including parallel ridges having thesame height, width, and spacing. In one embodiment, the ridges in asingle set of ridges can span the entire wafer. In another embodiment,different sets of ridges can be formed at different locations on thewafer. For example, each die region between scribe lines can have aparticular arrangement of ridge sets, with ridges in different setsrunning in different directions to provide device fabricationflexibility.

The invention will be more fully understood in view of the followingdescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, 1E, 1F, 1G, and 1H are various views of atransistor including a segmented channel region.

FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H, 2I, 2J, and 2K are steps in amanufacturing process for a transistor having a segmented channelregion.

FIGS. 3A, 3B, 3C, and 3D are top views of different corrugatedsubstrates that can be used in the manufacture of ICs that incorporatetransistors having segmented channel regions.

FIGS. 4A, 4B, 4C, 4D, and 4E are steps in a manufacturing process for anIC that incorporates transistors having segmented channel regions.

FIG. 5 is a flow diagram of a process for manufacturing an IC thatincorporates transistors having segmented channel regions.

DETAILED DESCRIPTION

Conventional metal-oxide-semiconductor field effect transistor (MOSFET)designs face significant problems as those designs are scaled down toimprove the cost and performance of integrated circuits (ICs). Inparticular, the techniques used to reduce static power consumption byminimizing source-to-drain leakage current (e.g., increased channeldoping, decreased gate-dielectric thickness, decreased source and drainjunction depths) tend to also decrease transistor performance bydecreasing on-current. By forming MOSFETs over a substrate havingprecisely-formed and regularly-spaced stripes (ridges of semiconductormaterial(s)), both high performance (i.e., high on-current) and lowstatic power consumption (i.e., low source-to-drain leakage current) canbe achieved with good uniformity. The stripes enable the formation ofsegmented channel regions that accommodate a wide range ofgate-electrode configuration options and also provide greaterperformance consistency between devices.

FIG. 1A shows a top view of an exemplary transistor 100 that includes asegmented channel region. Transistor 100 is formed on a substrate 190and is surrounded by device isolation material 193 (e.g., shallow trenchisolation), and includes a source 110, a drain 130, a gate 150, sidewallspacers 161 and 162, a source contact region 171, and a drain contactregion 172. Gate 150 (with a gate length LG) is located between source110 and drain 130 and is formed over a channel region 120 in substrate190. In various embodiments, gate 150 can be formed from anysemiconductor/conductor material, including doped silicon, dopedsilicon-germanium alloy, undoped or doped silicide, undoped or dopedgermanosilicide, metal, metal-nitride, conductive metal-oxide, or anycombination of layers of these materials, among others. Sidewall spacers161 and 162 lie over at least a portion of source 110 and drain 130,respectively, and serve to offset the gate 150 from source contactregion 171 and drain contact region 172, respectively. In variousembodiments, source contact region 171 and drain contact region 172 mayeach be comprised in part of a metal-semiconductor compound such assilicide, germanide, or germanosilicide.

As indicated by the dotted lines, channel region 120 includes multipleridges 191 that run between source 110 and drain 130. Ridges 191 areformed from at least one semiconductor material and may be homogenousstructures (e.g., silicon, silicon-germanium alloy, germanium,silicon-carbon alloy, compound semiconductor materials, or alignedcarbon nanotubes) or may have layers of different materials (e.g., asilicon layer on a dielectric layer or a silicon layer on asilicon-germanium layer). Ridges 191 are formed on an elevated baseregion 195 that rises from substrate 190, as shown in FIG. 1B. FIG. 1Bis a cross-sectional view of transistor 100 through view location A-A(rotated 90° for clarity). Each ridge 191 has a width W, and is spacedfrom adjacent ridges by a spacing SP. Furthermore, each ridge 191extends a height HR above elevated base region 195, which itself rises aheight HB from the adjacent surfaces 190-S of substrate 190.

Note that while four ridges 191 are depicted for exemplary purposes,transistor 100 can include any number of ridges 191, and that theparticular sizing, spacing, and quantity of ridges 191 (and also ofelevated base region 195) included in transistor 100 is determined bythe desired properties of transistor 100. Note further that becauseridges 191 are identified relative to substrate 190, ridges 191 continueto exist as “ridges” even covered with other materials (e.g., eventhough ridge isolation material 192, device isolation material 193, gatedielectrics 140, and gate 150 completely cover ridges 191, ridges 191are still considered to be ridges.)

In addition, while depicted as homogenous extensions of elevated baseregion 195 (and hence substrate 190) for exemplary purposes, ridges 191can comprise any construction (e.g., as described in greater detailbelow, each of ridges 191 can include multiple layers of differentsemiconductor or semiconductor and dielectric materials) and may even beformed from a different material(s) than elevated base region 195 and/orsubstrate 190. As described in greater detail below, each of ridges 191is a highly precise structure that therefore provides highlyquantifiable performance measures. Therefore, achieving a desiredperformance for transistor 100 simply entails incorporating anappropriate number of ridges 191 (e.g., if each ridge provides 0.1 mA ofon-current and the desired on-current for transistor 100 must be atleast 0.5 mA, five ridges 191 can be included in transistor 100).

Transistor 100 is isolated from adjacent devices by device isolationmaterial 193 (e.g., silicon dioxide, silicon nitride, or any otherdielectric material(s)), which extends down to surfaces 190-S ofsubstrate 190 (i.e., down to the bottom of elevated base region 195).Ridge isolation material 192 (which can be formed from the samematerial(s) or different material(s) than device isolation material 193)fills the inter-ridge regions to a distance HG below the top of ridges191. Gate 150 is formed over the top portions of ridges 191, separatedfrom those top portions by gate dielectric 140 (which can be formed fromany dielectric material(s), including silicon dioxide, siliconoxynitride, silicon nitride, hafnium dioxide, hafnium silicate,HfSiO_(x)N_(y), HfAlO_(x)N_(y), HfAlO_(x), zirconium dioxide, zirconiumsilicate, or other high-permittivity dielectric, or any combination oflayers of these materials, among others). Thus, when appropriatevoltages are applied to gate 150 and between source 110 and drain 130,each of ridges 191 conducts a portion of the total on-current that flowsthrough transistor 100.

Note that gate dielectric 140 and gate 150 “wrap” around the topportions of ridges 191 (i.e., gate dielectric 140 and gate 150 extenddown the sides of ridges 191 by recess distance HG). This wrappingconfiguration allows gate 150 to more effectively control the electricpotential distribution within channel region 120, and can thereforeenhance on-current while minimizing source-to-drain leakage current. Tofurther enhance performance, each ridge 190 can include a sub-surfaceheavily doped region 191P that provides a region of high dopantconcentration below the top surface of each ridge (as described ingreater detail below).

Note further that in various other embodiments, ridges 191 can exhibit amultilayered construction (i.e., two or more layers of differentmaterials). For example, each ridge 191 may include a semiconductorlayer formed over a dielectric layer (e.g., to reduce body leakage).Each ridge 191 may also include multiple layers of semiconductormaterials (e.g., to induce a desired stress within channel region 120).In addition, transistor 100 may include any other type of stressengineering structures, as indicated by optional stress engineeringstructure 155 (indicated by a dotted line). For example, stressengineering structure 155 could be a stressed capping layer formed oversource 110, drain 130, and gate 150 (and any intermediate structuressuch as sidewall spacers 161 and 162 shown in FIG. 1A) to induce adesired compressive or tensile stress within channel 120 in each ridge191 for enhancing carrier mobility.

FIG. 1C shows a cross-sectional view of transistor 100 through viewlocation B-B indicated in FIG. 1A. View location B-B provides across-sectional view running parallel to the direction of current flowbetween source 110 and drain 130 and through one of ridges 191, andtherefore indicates the full doping profiles in and around channelregion 120. As indicated in FIG. 1C, source 110 and drain 130 are dopedregions within ridge 191. Note that source 110 and drain 130 can beformed in portions of transistor 100 that may originally have beendiscrete ridges (i.e., continuous with ridges 191 in channel region 120)but were subsequently filled (as described in greater detail below) toprovide large planar source contact region 171 and drain contact region172, respectively, for the landing of metallic interconnects in theseregions.

Note further that source 110 and drain 130 can optionally includeshallow extensions such as lightly doped source 110-L and lightly dopeddrain 130-L, respectively, to reduce short-channel and hot-carriereffects. Typically, source and/or drain extensions such as lightly dopedsource 110-L and lightly doped drain 130-L are formed by performing ashallow ion implant operation after the formation of gate 150. Sidewallspacers 161 and 162 are then formed on each side of gate 150, and asubsequent higher-dose, deeper implant operation is performed. Sidewallspacers 161 and 162 (which can be formed from any dielectricmaterial(s), including silicon dioxide, silicon oxynitride, siliconnitride, hafnium dioxide, hafnium silicate, HfSiO_(x)N_(y),HfAlO_(x)N_(y), HfAlO_(x), zirconium dioxide, zirconium silicate, orother high-permittivity dielectric, or any combination of layers ofthese materials, among others) block dopant penetration into thesemiconductor, thereby allowing lightly doped source 110-L and lightlydoped drain 130-L, respectively, to remain as discrete shallowextensions after this second implant operation. Note that if corrugatedsubstrate is an SOI substrate (e.g., with ridges 191 formed on aninsulation layer), or if ridges 191 themselves include an insulatinglayer, the heavily doped regions of source 110 and drain 130 might notbe deeper than lightly doped source 110-L and lightly doped drain 130-L,respectively.

Note further that in various other embodiments, lightly doped source110-L and lightly doped drain 130-L (and/or source 110 and drain 130)may be formed from material(s) other than doped semiconductor material.For example, to reduce parasitic series resistance, lightly doped source110-L and lightly doped drain 130-L (and/or some or all of source 110and drain 130) may be formed from a metal-semiconductor compound (e.g.,silicide, germanide, or germanosilicide, among others). In oneembodiment, the regions of source 110 and drain 130 could be eitherundoped or doped prior to metal-semiconductor compound formation, sothat the metal-semiconductor compound material formed in those regionsmay be undoped or doped, respectively.

Note also that in various other embodiments, transistor 100 may notinclude sidewall spacers 161 and 162 and/or lightly doped source 110-Land lightly doped drain 130-L. Note further that lightly doped source110-L and/or lightly doped drain 130-L may or may not extend underneaththe edges of gate 150. Note further that due to the enhanced gatecontrol provided by the “wrapped” gate 150, in various otherembodiments, the source and drain extensions may be eliminated, so thatboth source 110 and drain 130 may be implemented as singly dopedregions. Note further that while depicted as extending below the bottomof ridges 191 for exemplary purposes, the depth D of source 110 anddrain 130 below the surface of ridge 191 can alternatively be less thanthe overall height HR of ridge 191 (i.e., depth D is less than ridgeheight HR), so that ridge isolation material 192 (shown in FIG. 1B),which starts from the base of ridge 191, can effectively reduce the areaof the junction between the source 110 and substrate 190, and the areaof the junction between the drain 130 and substrate 190, therebyreducing junction leakage and capacitance.

Note further that while ridge 191 is depicted as a homogenous structureextending from elevated base region 195 for exemplary purposes, ridge191 can exhibit any compositional structure. As noted above with respectto FIG. 1B, ridge 191 could exhibit a multilayered structure thatincludes at least one layer of a semiconductor material. In otherembodiments, ridge 191 could exhibit laterally changing materialcompositions. For example, channel region 120 (and the portion of ridge191 below channel region 120) could exhibit different semiconductormaterial(s) and/or construction from the surrounding portions of ridge191 (e.g., ridge 191 could include a dielectric region only underchannel 120).

FIG. 1D shows a cross-sectional view of transistor 100 through viewlocation C-C indicated in FIG. 1A. View location C-C runs between tworidges 191, parallel to the direction of current flow between source 110and drain 130. Therefore, FIG. 1D depicts gate 150 (and sidewall spacers161 and 162) extending down below the top surface of ridge 191.Specifically, gate 150 extends down to the level of ridge isolationmaterial 192. Note that because view location C-C runs between ridges191, the portions of source 110 and drain 130 on either side of gate 150(and sidewall spacers 161 and 162, if present) are actually fill regions191-F (i.e., regions formed by filling the space between the exposedportions of adjacent ridges 191, as described in greater detail below).

As noted above, the conventional method of reducing source-to-drainleakage current by increasing channel doping has the undesirable sideeffect of reducing channel carrier mobility, thereby reducing overallon-current. Therefore, alternative approaches have been developed totake advantage of the fact that the bulk of source-to-drain leakagecurrent occurs in regions where the electric field induced by the gateis limited, i.e., in the portion of the channel furthest from the gate.One approach to eliminate this leakage path is to use a steep retrogradechannel doping profile, such as the “pulse-shaped doping” described in“Scaling the Si MOSFET: From Bulk to SOI to Bulk”, by Ran-Hong Yan etal., IEEE Transactions On Electron Devices, vol. 39. no. 7, July 1992.In the pulse-shaped doping approach, a heavily doped region is formed atsome distance beneath the surface of a substrate (for example, byperforming a high-energy ion implant operation, in which the implantedions all penetrate to at least a desired depth below the surface). Thedopant concentration profile created in this manner starts off low atthe top surface of the substrate, then jumps to a high dopantconcentration (the “pulse”) at a desired distance below the surface, andthen eventually falls back to a lower concentration. Note that invarious other embodiments, the sub-surface heavy doping provided by theretrograde-doped region 191P can extend to any depth, and can evenextend into the bulk substrate region of substrate 190 (i.e., below thebases of ridges 191), though it is preferable for the heavily-dopedregion 191P to not extend past the depth of source 110 and drain 130 inorder to minimize junction capacitance and junction leakage current.

By combining appropriately positioned retrograde channel doping (asindicated by sub-surface heavily doped region 191P in FIGS. 1B and 1C)with the segmented channel construction of transistor 100, a lowsource-to-drain leakage current can be achieved while still providingrelatively high on-current performance.

Note that the change in doping concentration provided by sub-surfaceheavily doped region 191P will be relatively abrupt, but will generallynot be a precise step function. Instead, the dopant concentration willexhibit a relatively sharp gradient from the low dopant concentrationchannel region 120 to the high dopant concentration of retrograde dopedregion 191P. For explanatory purposes, the boundary of sub-surfaceheavily doped region 191P (i.e., the bottom of undoped or lightly dopedchannel region 120) can be considered to be the location at which thedopant concentration reaches 50% of the maximum dopant concentration insub-surface heavily doped region 191P.

As depicted in FIG. 1B, heavily doped regions 191P are ideally locatedsuch that the undoped or lightly doped channel region 120 in each ridge191 corresponds to the overlap R between gate 150 and each ridge 191. Inother words, the sub-surface heavily doped region 191P preferably startsat the point where gate 150 ends along each ridge 191 (i.e., at distanceHG below the top surface of ridge 191). This design can provide anoptimal trade-off between transistor performance and power consumption,since the channel region 120 in each ridge 191 is bounded on three sidesby gate 150 to maximize gate control to achieve high on-current, and isbounded by sub-surface heavily doped region 191P just below gate 150 tominimize source-to-drain leakage current. Note, however, that the dopantconcentration profile of the sub-surface heavily doped region 191P willtypically not be a sharp step function (i.e., the dopant concentrationwill not abruptly jump to the maximum dopant concentration level). Theactual dopant concentration profile of sub-surface heavily doped region191P will be a roughly exponential or Gaussian increase (until themaximum dopant concentration is reached). Therefore, benefits providedby sub-surface heavily doped region 191P can generally be maximized ifthe distance from the top surface of ridge 191 at which sub-surfaceheavily doped region 191P reaches 50% of the maximum dopantconcentration is equal to or less than distance HG. Note that theboundary of sub-surface heavily doped region 191P generally should notbe located too close to (e.g., less than 5 nm away from) the top surfaceof ridge 191, however, otherwise the transistor on-state drive currentwill be degraded. Thus, if distance HG is very small (e.g., less than 5nm), then sub-surface heavily doped region 191P should start below thepoint where gate 150 ends along each ridge 191.

Note that any other techniques for creating sub-surface heavily dopedregions can be used. For example, FIG. 1E shows a cross-sectional viewof a transistor 100-1 that is substantially similar to transistor 100described with respect to FIGS. 1A-1D, except that rather thanincorporating a retrograde channel doping profile (191P), transistor100-1 includes sub-surface heavily doped regions 191P-HS and 191P-HD.Sub-surface heavily doped regions 191P-HS and 191P-HD are formed using“halo” doping adjacent to lightly doped source 110-L and lightly dopeddrain 130-L, respectively. By creating a high dopant concentration atthe source and drain extensions, this halo doping can reduce shortchannel effects, thereby minimizing source-to-drain leakage current.FIG. 1F shows a cross-sectional view of a transistor 100-2 that issubstantially similar to transistor 100-1 shown in FIG. 1E, excepttransistor 100-2 includes sub-surface heavily doped regions 191P-PS and191P-PD beneath lightly doped source 110-L and lightly doped drain130-L, respectively. These “pocket” doped regions can provide the sametype of leakage current reduction described with respect to sub-surfaceheavily doped regions 191P-HS and 191P-HD described with respect to FIG.1E.

Table 1 shows sample data for comparing the performance (on-state drivecurrent and off-state source-to-drain leakage current, each normalizedto the transistor layout width) of various n-channel implementations oftransistor 100 (rows 1, 2, 3, 4, 5, and 6) against the performancespecifications with no carrier mobility enhancement as published in theInternational Technology Roadmap for Semiconductors (ITRS), 2003 Edition(rows 7 and 8). Each of the implementations of transistor 100 is basedon a fundamental set of implementation values, including a single ridge191 in the channel region, a 20 nm spacing between ridges 191 (i.e., thetotal layout width of the simulated transistor 100 is the ridge width Wplus 20 nm), a thickness for gate dielectric 140 equivalent to 1.2 nm ofSiO₂, an undoped channel, a heavily p-type doped (2×10¹⁹ cm⁻³ boron)pulse doped region starting precisely at the end of the gate overlap(i.e., at a distance HG below the surface of ridge 191), no stress-basedmobility enhancement, and singly doped source/drain regions.

TABLE 1 W LG HG Ion Ioff No. Description (nm) (nm) (nm) (mA/μm) (nA/μm)1 Slightly 20 20  5 0.5 3 × 10⁻⁶ Recessed 2 Moderately 20 20 10 0.6 0.4Recessed 3 Very Recessed 20 20 15 0.98 500 4 Longer 20 40 20 0.8 8 ×10⁻⁴ Channel 5 Wider Ridge 40 20 10 0.82 2.2 6 “FinFET” 10 20 20 1.30 177 ITRS High NA 20 NA 0.8 70 Performance 8 ITRS Low NA 20 NA 0.58 0.06Standby Power

As indicated in Table 1, design number 1, which incorporates a ridgewidth of 20 nm, a gate length of 20 nm, and a recess distance of 5 nm (a“Slight Recess”), provides an on-state drive current I_(on) of 0.5 mA/μmand an off-state source-to-drain leakage current I_(off) of 3×10⁻⁶nA/μm. Note that I_(on) and I_(off) are listed in terms of current permicron layout width (in the direction transverse to the direction ofcurrent flow) to normalize the current values. Thus, by implementingtransistor 100 with just a slight wrapping of gate 150 around ridge 191,a very low off-state leakage current is achieved, but the on-state drivecurrent is somewhat low. Increasing the recess distance HG to 10 nm indesign number 2 provides an increase in I_(on) to 0.6 mA/μm, at thetrade-off of increasing I_(off) to 0.4 nA/μm. Further increasing recessdistance HG to 15 nm in design number 3 provides a significant jump inI_(on) to 0.98 mA/μm, but increases I_(off) to 500 nA/μm. Thus,implementing transistor 100 using values similar to design number 3would generally be best for high performance circuits, whereasimplementing transistor 100 using values similar to design number 1would be best for ultra-low power circuits.

As indicated by the performance values provided for design numbers 1-3,transistor 100 allows the relationship between on-current I_(on) andoff-current I_(off) to be adjusted via recess distance HG, i.e. thedepth of the sub-surface heavily doped region 191P. In contrast, theI_(on)/I_(off) relationship in conventional transistors is typicallymodified by adjusting the doping concentration within the channel regionto achieve a particular threshold voltage. Because dimensional control(i.e., control over recess distance HG and the location of sub-surfaceheavily doped region 191P) can be more precise than dopant concentrationcontrol (i.e., control over the number of dopant atoms in the channelregion), transistor 100 can significantly ease the difficultiesassociated with achieving a particular combination of on-current I_(on)and off-current I_(off).

Adjusting other parameters of transistor 100, such as increasing gatelength (design number 4, “Longer Channel”) or increasing ridge width(design number 5, “Wider Ridge”) can provide additional adjustmentcontrol over on-current I_(on) and off-current I_(off). Design 6(“FinFET”) approximates a vertical transistor design that has beendeveloped in an effort to overcome the aforementioned limitations ofconventional MOSFET transistors. A FinFET incorporates a high aspectratio structure (fin) extending above the substrate surface that formsthe channel region for the transistor. A gate is formed transverse tothe fin and down both sides of the fin, thereby providing a “doublegate” type of structure (i.e., the gate electrode induces an electricfield from both sides of the fin in the channel region). As indicated bythe values for design number 6, a FinFET can achieve high on-currentI_(on) and a relatively low off-current I_(off). However, the highaspect ratio fin coupled with a deep recess distance (essentially thefull height of the fin channel region) can make the FinFET substantiallymore difficult to manufacture than transistor 100 (which can be formedusing standard manufacturing processes as described in greater detailbelow).

Transistor 100 therefore provides a highly manufacturable structuraldesign that still allows a great deal of performance enhancement andpower savings capabilities. Note that the raised construction of ridges191 can also beneficially minimize stress induced within the channelregion of transistor 100 by the insulation material surrounding thedevice. Material stress can significantly affect the performance of atransistor (both negatively and positively). Therefore, it is desirableto be able to accurately define the stress within the channel region ofa transistor. Due to the raised nature of ridges 191, any undesirablestress at the base of ridges 191 will typically be significantly reducedwithin the top portions of ridges 191 wherein the active region oftransistor 100 resides (i.e., from the tips of ridges 191 down to adistance HG). Furthermore, stress within transistor 100 is reduced evenmore by the fact that ridges 191 are formed on elevated base region 195that further removes channel region 120 from the regions of higheststress (where device isolation material 193 meets elevated base region195). Therefore, the elevated, ridged construction of transistor 100 cansignificantly reduce undesirable stress within transistor 100 (versusconventional transistor designs). In general, beneficial stress relieffrom and adequate electrical isolation by device isolation material 193can be provided when the depth of device isolation material 193 belowthe base of ridges 191 is at least equal to the height of ridges 191(i.e., elevated base height HB is greater than or equal to ridge heightHR). However, optimal stress/electrical isolation may be provided bysignificantly higher base height/ridge height ratios (e.g., base heightHB is equal to 5× ridge height HR). Note also that since ridges 191 canbe defined and manufactured with a high degree of precision (asdescribed in greater detail below), beneficial stress within each ridge191 can be accurately induced (e.g., by forming ridges 191 as silicon onsilicon-germanium stacks) to allow transistor 100 to achieve a desiredperformance simply by incorporating an appropriate number of ridges 191.

Note further that almost any enhancements available to conventionalMOSFET designs can be applied to transistor 100. For example, in oneembodiment, the gate of transistor 100 may simply be flush with the topsurfaces of ridges 191 (i.e., distance HG shown in FIG. 1B is zero).FIG. 1G shows an alternative cross-sectional view of transistor 100(labeled as transistor 100-3 for clarity) through view location A-Aindicated in FIG. 1A. The cross-sectional view of transistor 100-3 issubstantially similar to the cross-sectional view of transistor 100shown in FIG. 1B, except that in transistor 100-3, ridge isolationmaterial 192-3 extends all the way up the sides of ridges 191, and gate150-3 (and gate dielectrics 140-3) does not wrap around the top portionsof ridges 191. The sub-surface heavy doping provided by theheavily-doped region 191P begins at some depth below the top surface ofridges 191, and can extend to any depth, though it is preferable for theheavily-doped region 191P to not extend past the depth of source 110 anddrain 130 in order to minimize junction capacitance and junction leakagecurrent.

In another embodiment, the segmented channel construction of transistor100 can be incorporated into a device formed on an SOI substrate. FIG.1H shows another alternative cross-sectional view of transistor 100(labeled as transistor 100-4 for clarity) through view location A-Aindicated in FIG. 1A. Transistor 100-4 includes ridges 191-4 formed onthe insulator layer 192-4 of an SOI substrate 195-4. Gate dielectrics140-4 are formed over each of ridges 191-4, over which gate 150-4 isformed. Note that transistor 100-4 does not require the ridge isolationmaterial 192 shown in FIG. 1B, because insulator layer 192-4 providesthe same electrical isolation. Note further that depending on the heightof ridges 191-4, pulse-shaped doping may or may not be necessary toreduce source-to-drain leakage for transistor 100-4, due to thechannel-bounding effect of insulator layer 192-4.

Ridges 191 in transistor 100 ideally exhibit a high degree of regularityand consistency to allow optimal functioning of transistor 100. In otherwords, each of ridges 191 should ideally be dimensionally consistentwith every other ridge 191. Furthermore, ridges 191 should be relativelynarrow and relatively tightly spaced to allow for maximum flexibility intransistor design and layout efficiency in an IC. For example, it may bedesirable to set ridge width W_(R) and ridge spacing SP each to theminimum gate length (e.g., 35 nm) for transistors in the IC. However,conventional lithographic methods used in semiconductor manufacturingare not able to easily provide such fine-pitched features. Specifically,the optical lithography methods used to define structures in modernsemiconductor manufacturing processes use an exposure wavelength of 193nm, and such methods can only directly produce structures down to ˜45 nmin lateral dimension through the use of various optical techniques thatattempt to compensate for the lack of actual exposure resolution. Forexample, techniques such as optical proximity correction (OPC) and phaseshift masking (PSM) make use of modified masks that make use ofdiffraction and interference effects to form pattern features that aresmaller than the wavelength of the exposure light.

Advantageously, by forming transistor 100 on a set of pre-existingridges 191, many of the limitations associated with conventionallithographic methods used in semiconductor manufacturing can beovercome. For example, FIG. 2A shows an exemplary corrugated substrate190 that includes a set of ridges 191. Each of ridges 191 has a heightHR, a width W, and a spacing between ridges SP. Because ridges 191 aremade prior to any specific device patterning, various processingtechniques can be used to generate ridges 191 with a high degree ofaccuracy and regularity. For example, imprint lithography is a techniquein which a master stencil is precisely patterned using electron-beamlithography. The master stencil is then used to pattern wafers (e.g., byimprinting a resist pattern onto a wafer), thereby enabling theformation of precise, sub-wavelength features on those wafers. Due tothe complexity of most IC layouts, imprint lithography is generally notpractical for use on production wafers. However, the technique is idealfor creating regular, repeating patterns on a wafer, such as ridges 191.The use of imprint lithography can allow ridges 191 to be created withextremely precise and regular dimensions, thereby avoiding the inherentinaccuracies associated with optical lithography. Other techniques forforming ridges 191 (such as spacer lithography described in Y.-K. Choiet al., “A spacer patterning technology for nanoscale CMOS,” IEEETransactions on Electron Devices, Vol. 49, No. 3, pp. 436-441, 2002, inwhich vertical thin films are created along the sidewalls of sacrificialfeatures, which are subsequently etched away) will be readily apparent.

Note that while ridges 191 are described as being formed from the samematerial as the underlying bulk substrate (i.e., the non-ridged portionof corrugated substrate 190) for exemplary purposes, according tovarious other embodiments of the invention, ridges 191 can compriseanother semiconductor material or materials. For example, each ridge 191could include a silicon layer formed over a silicon-germanium alloylayer. Alternatively, each ridge 191 could include a semiconductor layerformed over an insulator layer. Furthermore, according to various otherembodiments, ridges 191 can include any type of semiconductor material(e.g., compound semiconductors or carbon nanotubes).

To prepare a corrugated substrate 190 for semiconductor devicefabrication, a ridge isolation material 192 is formed around and betweensemiconductor ridges 191, as shown in FIG. 2B. A planarization operationmay be used to ensure that the top surface of ridge isolation material192 is aligned with the tips of ridges 191. Note that if corrugatedsubstrate is an SOI substrate (e.g., with ridges 191 formed on aninsulation layer), or if ridges 191 themselves include an insulatinglayer, ridge isolation material 192 can be eliminated.

An active region 102 (indicated by the dotted line) is then defined tospecify the location for the final transistor(s). Just as in processesused to form conventional ICs, the areas in which the semiconductordevices (i.e., transistors, resistors, and/or capacitors) and/or localinterconnects formed in semiconductor material are to be formed can bemasked (typically by a lithographic operation). Note that while activeregion 102 is depicted as spanning four ridges 191 for exemplarypurposes, in various other embodiments active region 191 can cover anynumber of ridges 191, depending on the desired characteristics of thefinal transistor(s) 100. For example, active region 102 could span asingle ridge 191, thereby allowing formation of the final transistor 100as a FinFET.

Once active region 102 is defined, ridges 191 and ridge isolationmaterial 192 can be selectively removed in the “field” areas surroundingthe active areas (typically by one or more etch operations), as shown inFIG. 2C. This etch operation(s) may reduce the field areas of substrate190 to a depth greater than the ridge height HR, and it may alsopartially or completely remove the ridge isolation material 192 in thefield regions. Note that elevated base region 195 can be formed byallowing the etch operation(s) to remove material from substrate 190below the base of ridges 191 in the field regions. Note further that ifa single etch is used, the subsequently formed surface 190-S ofsubstrate 190 may exhibit a slightly irregular profile, due to thetypically different etch rates of ridge isolation material 192 (e.g.,silicon oxide) and ridges 191/substrate 190 (e.g., silicon).

After the active region formation step of FIG. 2C, the field regions arefilled with device isolation material 193, as shown in FIG. 2D. Just asdescribed above with respect to the formation of ridge isolationmaterial 192, a planarization operation can be performed to ensure thatthe top surface of device isolation material 193 is aligned with the topsurfaces of ridges 191. Note that the depth of device isolation material193 is determined by the depth to which the active region definitionoperation reduces substrate 190 (i.e., distance HB below the base ofridges 191). In one embodiment, device isolation material 193 can beselected to have an etch rate similar to that of ridge isolationmaterial 192, thereby allowing uniform (subsequent) selective etching toexpose the tips of ridges 191, as described in greater detail below.Note that if corrugated substrate is an SOI substrate (e.g., with ridges191 formed on an insulation layer), or if ridges 191 themselves includean insulating layer, device insulation material 193 can be eliminated.

Note further that in one embodiment, ridges 191 may be selectivelyetched, and the resulting channels defined by the remaining ridgeisolation material 192 and device isolation material 193 can be filledwith one or more layers of semiconductor material (e.g., silicon,germanium, or silicon-germanium alloy), thereby creating preciselyvertically engineered semiconductor ridges. Because the defect densityof epitaxially grown semiconductor films is dramatically reduced byspatial confinement, this “etch-refill” approach can provide significantbenefit for manufacturing heterostructure semiconductor channel filmswith low defect density (i.e. high yield). In one embodiment, thelayering of semiconductor materials having different lattice constantscan provide beneficial stress within ridges 191 to improve final deviceperformance.

Next, in FIG. 2E, ridge isolation material 192 and field insulationmaterial 193 may optionally be selectively etched a distance HG belowthe top surfaces of ridges 191. The exposed tips of ridges 191 are thencovered with gate dielectric layer(s) 140, as shown in FIG. 2F, and agate 150 is formed over the desired channel region for transistor 100,as shown in FIG. 2G.

Note that in some embodiments, ridge isolation material 192 and deviceisolation material 193 may be selectively etched in the channel regionbelow the top surfaces of ridges 191 to expose the top or sidewalls ofone or more buried layers within the ridges, and the one or more buriedlayers within the ridges may then be selectively removed in this regionso that one or more remaining semiconductor layers within the ridgesform bridge(s) in the channel region. Then the exposed surfaces of thesemiconductor layers are covered with gate dielectric 140 and gate 150,which as a result wrap around the semiconductor bridges (which alsore-forms the portions of ridges 191 removed during the selective etchprocess), as described in “Silicon-on-Insulator ‘Gate-All-AroundDevice’”, by J. P. Colinge et al., International Electron DevicesMeeting Technical Digest, pp. 595-598, 1990 and also in “A Novel Sub-50nm Multi-Bridge-Channel MOSFET (MBCFET) with Extremely HighPerformance,” by S.-Y. Lee et al., Symposium on VLSI Technology Digestof Technical Papers, pp. 200-201, 2004. Note that if corrugatedsubstrate is an SOI substrate (e.g., with ridges 191 formed on aninsulation layer), or if ridges 191 themselves include an insulatinglayer, then the initial isolation material etch is not necessary.

At this point, an optional light doping operation (e.g., a low-dose ionimplantation operation) can be performed on the exposed tips of ridges191 to form a lightly doped source (i.e., 110-L in FIG. 1C) and alightly doped drain (i.e., 130-L in FIG. 1C) for transistor 100.Sidewall spacers 161 and 162 may then be formed on either side of gate150, as shown in FIG. 2H, after which a heavier doping operation may beperformed to form the deeper source (110 in FIG. 1C) and drain (130 inFIG. 1C) regions for transistor 100. The exposed portions of gatedielectric layer(s) 140 (i.e., the portions of gate dielectric layer(s)140 that are not covered by gate 150) may then be removed as shown inFIG. 2I.

Then, to simplify subsequent source and drain contact formation, thespaces between the exposed portions of ridges 191 can optionally befilled with semiconductor material (which can either be the samematerial from which ridges 191 are formed or one or more differentsemiconductor materials), as shown in FIG. 2J. Note that sidewallspacers 161 and 162 can help to isolate gate 150 from the fill materialdeposited or grown in FIG. 2J. Note that this fill operation may involvefilling just the spaces between ridges 191, forming a blanket layer ofsemiconductor material over ridges 191, “growing” additional material onridges 191, or any combination of the above. The semiconductor materialmay be doped in-situ during the deposition/growth process, or it may bedoped with a separate doping operation (e.g., a high-dose ionimplantation operation). Note that any desired well and/or channeldoping (e.g., pulse-shaped doping, halo doping, or pocket doping, amongothers) process steps could be performed any time up to this point. Notefurther that as described with respect to FIG. 1C, any source/drainextensions (and/or source/drain regions) may be transformed into ametal-semiconductor compound (e.g., silicide, germanide, orgermanosilicide, among others), either before or after the filloperation.

Note further that the physical characteristics of source 110 and drain130 can vary depending on the process used to create the fill materialaround ridges 191. For example, the fill material (as described withrespect to the formation of source 110 and drain 130 in FIG. 2J) may beformed using epitaxial growth, thereby causing source 110 and drain 130to exhibit a very homogeneous structure. Alternatively, conformaldeposition may be used such that source 110 and drain 130 exhibit a“striped” structure, with ridges 191 alternating with the new fillmaterial. In such a circumstance, source 110 and drain 130 can includediscrete structures that are continuous with ridges 191 in the channelregion.

Note also that in one embodiment, the exposed portions of ridges 191 canbe etched prior to epitaxial growth of the filler material. By thengrowing an appropriate semiconductor material over the reduced-height(or completely eliminated, if the etch removes material down to elevatedbase region 195 shown in FIGS. 1B-1D or below) portions of ridges 191, adesired stress can be induced in the portions of ridges 191 beneath gate150 (i.e., in the channel region of transistor 100).

For example, by etching the exposed portions of ridges 191 and thengrowing silicon-germanium alloy (Si_(1-x)Ge_(x)) in the source/draincontact regions, compressive uniaxial stress can be induced in thechannel region to enhance the mobility of holes, thereby providingenhanced p-channel MOSFET performance. On the other hand, growingsilicon-carbon alloy (Si_(x)C_(1-x)), rather than silicon-germanium,would induce tensile uniaxial stress in the channel region to enhancethe mobility of electrons, thereby providing enhanced n-channel MOSFETperformance. As noted above, the confinement of epitaxial growth tosmall-dimensioned regions (such as source 110 and drain 130 in FIG. 2J)helps to reduce the defect density in the epitaxially grown material,which allows maximum stress levels to be achieved. This in turn enablesthe generation of consistent stress levels from transistor totransistor, thereby enhancing the uniformity of transistor performanceacross an IC.

Note that in another embodiment, a portion of the ridges underneath thegate may be selectively removed and optionally refilled (e.g. with aninsulating material), prior to epitaxial growth of the filler material,in a manner similar to that described in “Silicon-on-Nothing (SON)—anInnovative Process for Advanced CMOS”, by M. Jurczak et al., IEEETransactions on Electron Devices, Vol. 47, No. 11, pp. 2179-2187,November 2000. Note that in another embodiment, the etched portions ofridges 191 (on either side of gate 150) can each be covered with ablanket layer of semiconductor material (different than the ridgematerial) to define the regions for source 110 and drain 130.

In any case, to complete transistor 100, source contact region 171 anddrain contact region 172 are formed over source 110 and drain 130,respectively, and directly abutting sidewall spacers 161 and 162,respectively, as shown in FIG. 2K. Note that while contacts can be madeto the exposed ridges 191 (in which case the source contact region 171and drain contact region 172 would simply consist of the exposedportions of ridges 191) shown in FIG. 2I without undue difficulty,device manufacturers generally prefer to form contacts on planarsurfaces, such as depicted for source 110 and drain 130 in FIGS. 2J and2K. In various embodiments, source contact region 171 and drain contactregion 172 may each be comprised in part of a metal-semiconductorcompound such as silicide, germanide, or germanosilicide to providelower contact resistance. Note that according to various embodiments,additional stress engineering structures (e.g., a stressed capping layerover gate 150, source 110, and drain 130) can be subsequently formed ontransistor 100 (as described with respect to FIG. 1B).

As described above with respect to FIG. 2A, by creating ridges 191 asstandalone structures prior to discrete device definition, ridges 191can be formed with a high degree of precision (±15% tolerances andbetter) using techniques that would not necessarily be suitable forgeneral IC production (e.g., imprint lithography and spacerlithography). In one embodiment, a semiconductor wafer can be fullypatterned with such ridges, thereby allowing subsequent formation oftransistor(s) 100 at any desired location on the wafer. For example,FIG. 3A shows a top view of a wafer 390-A that includes an array ofridges 391-A running across almost the entire wafer surface. Ridges391-A are substantially similar to ridges 191 described previously, andhave a predetermined height (HR in FIG. 2A), width (W in FIG. 2A),spacing (SP in FIG. 2A), and composition (e.g., silicon,silicon-germanium, silicon on silicon-germanium, or carbon nanotubes,among others). By forming ridges at the wafer level, IC production costsare minimally impacted, since this type of simple bulk patterning ismuch less complex (and therefore much less expensive) than the localizedfeature formation performed during subsequent IC processing. Note thatin one embodiment, wafer 391-A can include ridge isolation material(e.g., ridge isolation material 192 shown in FIG. 2B) between ridges391-A.

Note further that in various other embodiments, a corrugated substratecan include localized groupings of parallel ridges, rather than thecontinuous ridges 391-A that span the entire wafer surface as shown inFIG. 3A. For example, FIG. 3B shows another embodiment of a corrugatedsubstrate 390-B that includes localized ridge sets 395. Each localizedridge set includes ridges 391-B that exhibit the same dimensional andphysical consistency as described with respect to ridges 391-A shown inFIG. 3A, but are discontinuous across scribe lines 399, which cansimplify subsequent IC formation and wafer dicing operations. Therefore,each die location on corrugated substrate 390-B (i.e., each locationwhere an IC is to be formed) includes a separate ridge set 395. Asdescribed with respect to FIG. 3A, ridge sets 395 can also include ridgeisolation material between ridges 391-B. Note that in some embodiments,within each ridge set 395, localized groupings of ridges 391-B mayexhibit different material compositions (as described in greater detailbelow with respect to FIG. 4A).

Note further that while ridges 391-B are all shown running in the samedirection for exemplary purposes, according to various otherembodiments, a corrugated substrate can include multiple localized ridgesets, wherein the ridges in different sets run in different directions.For example, FIG. 3C shows a top view of an alternative localized ridgeset 395-C that could be implemented in place of localized ridge sets 395in FIG. 3B. Localized ridge set 395-C includes a ridge set includingparallel ridges 391-C1, a ridge set including parallel ridges 391-C2, aridge set including parallel ridges 391-C3, and a ridge set includingparallel ridges 391-C4. As described with respect to FIG. 3B, optionalridge isolation material can separate the ridges in each of the ridgesets. Parallel ridges 391-C1 and 391-C4 run perpendicular to parallelridges 391-C2 and 391-C3. Any other arrangement of ridges can providethe benefits described above, so long as the ridges in any particularset of parallel ridges are longer than the critical dimension (i.e., theminimum geometry) of the devices being formed using the ridges. Note,however, that the ridges themselves may actually be thinner than thecritical dimension (since the ridges can be manufactured usingtechniques other than those ordinarily used in actual device production,as described above). Note further that while the areas occupied byparallel ridges 391-C1, 391-C2, 391-C3, and 391-C4 are depicted as beingroughly equal for exemplary purposes, the different ridge groupingswithin a die location (i.e., between scribe lines) can exhibit anydesired sizing relationship with one another.

Note further that a corrugated substrate can include large planarsemiconductor surface regions. For example, FIG. 3D shows a top view ofan alternative localized ridge set 395-D that could be implemented inplace of localized ridge sets 395 in FIG. 3B. Localized ridge set 395-Dincludes a ridge set including parallel ridges 391-D1 (separated byoptional ridge isolation material), a ridge set including parallelridges 391-D2 (separated by optional ridge isolation material), andplanar (unridged) semiconductor surface regions 391-F1 and 391-F2.Conventional planar semiconductor devices (i.e., transistors, resistors,and/or capacitors) can be formed in these planar semiconductor surfaceregions 391-F1 and 391-F2 simultaneously with corrugated-semiconductordevices, e.g. by using the fabrication process flow described above.Note that while planar semiconductor surface regions 391-F1 and 391-F2are depicted as covering roughly the same area as parallel ridges 391-D1and 391-D2 for exemplary purposes, groupings of parallel ridges andplanar regions can exhibit any relative sizing. Note further that aportion of a corrugated substrate can be considered a planar region solong as that portion provides an unridged area that is at least as wideas two ridges plus the spacing between those two ridges.

Ideally, a corrugated substrate will include sets of parallel ridgesthat cover an area at least as large as a basic functional block (e.g.,a set of devices that performs a particular logic function). Acorrugated substrate providing ridge sets sized in this manner canbeneficially minimize the need for additional interconnect wiringbetween devices within functional blocks. Larger ridge sets can likewiseminimize interconnect wiring requirements between functional blocks.

For example, FIG. 4A shows a corrugated substrate 490 that includes aset of parallel ridges 491, optionally supplied with ridge isolationmaterial 492 present between ridges 491 (alternatively, a dielectricformation operation can be performed to form ridge isolation material492, in a manner substantially similar to that described with respect toFIG. 2B). Ridges 491 are substantially similar to ridges 191 describedpreviously, and have a predetermined height (HR in FIG. 2A), width (WRin FIG. 2A), spacing (SP in FIG. 2A), and composition (e.g., silicon,silicon germanium, silicon on silicon-germanium, or carbon nanotubes,among others). Active regions 401 (indicated by the dotted lines)represent locations where functional elements of a circuit are to beformed.

Note that while ridges 491 are dimensionally very similar, thecomposition of ridges 491 can vary. For example, a ridge group 491Acould include a top silicon layer (e.g. a silicon ridge) providing (110)surface crystalline orientation, and a ridge group 491B could include atop silicon layer (e.g., an SOI ridge) providing (001) surfacecrystalline orientation. Then, if active regions 401-1 and 401-2represent regions in which PMOS devices are to be formed, the ridges 491in ridge group 491A provide a surface crystalline orientation optimizedfor PMOS performance. Similarly, if active regions 401-3 and 401-4represent regions in which NMOS devices are to be formed, the ridges 491in ridge group 491B provide a surface crystalline orientation optimizedfor NMOS performance.

To begin the manufacturing process, the portions of ridges 491 (and allor part of ridge isolation material 492) that lie outside of the activeregions 401 are removed (e.g., the portions of ridges 491 and insulationmaterial 492 within active regions 401 could be masked, and the unmaskedportions of ridges 491 and ridge isolation material 492 could then beetched away, as described with respect to FIG. 2C). Non-ridge portionsof substrate 490 are then filled with device insulation material 493(e.g., shallow trench isolation), as shown in FIG. 4B (e.g., asdescribed with respect to FIG. 2D), and ridge isolation material 492 anddevice isolation material 493 can optionally be etched to expose the topportions of the remaining ridges 491 (e.g., as described with respect toFIG. 2E). The exposed portions of ridges 491 are then covered with gatedielectric layer(s) 440 (as described with respect to FIG. 2F).

Next, in FIG. 4C, gates 450 are formed over desired transistor channellocations, as described with respect to FIG. 2G. At this point, anoptional doping operation (e.g., ion implantation operation) can beperformed to create source/drain extensions (e.g., 110-L and 130-L inFIG. 1C) within the ridges in the regions not covered by gates 450.Sidewall spacers (not shown for clarity) may then be formed along thesidewalls of gates 450 (e.g., as described with respect to FIG. 2H),after which a heavier doping operation can be performed to form deepersource and drain regions (e.g., 110 and 130 in FIG. 1C). The portions ofgate dielectric layers 440 that are not covered by gates 450 may then beremoved (e.g., etched selectively off of ridges 491, as described withrespect to FIG. 2I)). The exposed portions of ridges 491 can befilled-in with semiconductor material to form large source-drain contactregions 415 and semiconductor interconnects 416, as shown in FIG. 4D(e.g., as described with respect to FIG. 2J). The source-drain contactregions 415 can be doped in-situ during the deposition/growth of thesemiconductor material, or they may be doped with a separate dopingoperation (e.g., a high-dose ion implantation operation), to completethe transistors in the circuit (e.g., transistors 400-1 and 400-2). Inaddition, any desired well and/or channel doping (e.g., pulse-shapeddoping) could be performed on ridges 491 (at any time up to this point).Furthermore, any desired metal-semiconductor compound formation insource/drain extension regions (and/or source/drain regions) can beperformed. For reference purposes, the portions of ridges 491 in thechannel regions of the transistors are indicated by the lightly shadedrectangles in gates 450 in FIG. 4D. A metal-semiconductor compound(e.g., silicide, germanide, or germanosilicide) may be formed insource-drain contact regions 415 (as described with respect to FIG. 2K)to reduce contact resistance. Note that if the gate “overhang” distanceHG (e.g., as shown in FIGS. 1B and 2E) for a given transistor(s) in FIG.4D is greater than the ridge width W (e.g., as shown in FIGS. 1B and 2A)of that transistor, then that transistor would essentially be a FinFET.In any case, to complete the IC, standard passivation, contactformation, metallization, and post-metallization annealing (PMA) canthen be performed to complete circuit 408 depicted in FIG. 4E(metallization not shown for clarity).

As noted above, the source-drain contact regions 415 consisting of“filled” ridges 491 provide reliable landing locations for contacts 405(although contacts could also be made to the original ridges 491themselves). Furthermore, the semiconductor interconnects 416 formed inthis manner provide device-level electrical connections. Consequently,the metallization requirements for circuit 408 are reduced, which canreduce cost and provide greater interconnect routing flexibility in themetal layer(s) of circuit 408. Note that in one embodiment, transistorsformed along common ridges 191 (e.g., transistors 400-1 and 400-2),could include unfilled ridges 191 to provide an electrical connectionbetween the transistors.

Note further that due to the use of a corrugated substrate (490) in theformation of circuit 408, the channel segments (ridges 491) in adjacenttransistors will always be closely aligned. For example, each of theeight transistors running across the bottom of circuit 408 (formed atgates 450) includes a channel segment aligned along a centerline CL.Such an arrangement is inevitable, since each of those channel segmentswas originally part of a single ridge 491 (i.e., ridge 491-1 shown inFIG. 4A). Each channel segment along centerline CL can easily exhibitdimensional consistency and alignment accuracy within 5% from segment tosegment (i.e., the widths and centerlines of the channel segments willall be within 5% of the widths and centerlines, respectively, of all theother channel segments). In contrast, a circuit manufactured using aconventional (non-corrugated) substrate will not exhibit the same degreeof dimensional consistency and channel alignment, due to the lack ofsimilar alignment constraints in the design and manufacturing process,and more importantly, due to inherently irregular patterns defined byoptical lithography in IC manufacturing processes.

FIG. 5 shows a flow diagram of the manufacturing process described withrespect to FIGS. 2A-2I and 4A-4E. First, in an optional “CREATECORRUGATED SUBSTRATE” step 505, a corrugated substrate (e.g., 190 inFIG. 2A, 390-A in FIG. 3A, 390-B in FIG. 3B, and 490 in FIG. 4A) isformed using a high-precision manufacturing technique (e.g., imprintlithography or spacer lithography). Alternatively, a pre-made corrugatedsubstrate can be used. Step 505 can also include a ridge isolationmaterial formation operation (e.g., if isolation material is notincluded in the pre-made corrugated substrate).

Then, the active regions for the circuit (i.e., regions in which devicesand optionally semiconductor interconnects are to be formed) are definedin a “DEFINE ACTIVE REGIONS” step 510 (as described with respect toFIGS. 2B and 4A). The ridges (and all or part of the ridge isolationmaterial) outside of the active regions are then removed (e.g., etchedaway) in a “REMOVE UNUSED RIDGES” step 515 (as described with respect toFIGS. 2C and 4B), and device isolation material (e.g., device isolationmaterial 493 in FIG. 4B) can be formed in the cleared field regions ofthe wafer in an optional “INSULATION FILL” step 520 (as described withrespect to FIG. 2D). In one embodiment, the insulation layer can beformed over the ridges, and can subsequently be planarized down to thesurface level of the ridges.

Top portions of the ridge isolation material and the device isolationmaterial can then be removed in an optional “RECESS INSULATION” step 525to expose top portions of the ridges (as described with respect to FIGS.2E and 4B). Optional well/channel doping (e.g., pulse-shaped doping) canbe performed at this point in a “CHANNEL/WELL DOPING” step 530, or atany point before “METALLIZATION” step 575. The exposed portions of theridges can then be coated with a gate dielectric layer in a “GATEDIELECTRIC FORMATION” step 535 (as described with respect to FIGS. 2Fand 4B), and gates can be formed over the desired portions of the coatedridges in a “GATE FORMATION” step 540 (as described with respect toFIGS. 2G and 4C). If desired, source/drain extensions can be formed atthis point in an optional “SOURCE/DRAIN EXTENSION DOPING” step 545 (asdescribed with respect to FIGS. 2G and 4C). Sidewall spacers can beformed along the sidewalls of the gates in an optional “SIDEWALL SPACERFORMATION” step 550 (as described with respect to FIGS. 2H and 4C).Optional halo or pocket doping can be performed at this point in anoptional “HALO DOPING” step 555 (e.g., as described with respect toFIGS. 1E and 1F). The unused portions of the gate dielectric layers(i.e., the portions not separating the gates from the ridges) can thenbe removed in an optional “GATE DIELECTRIC REMOVAL” step 560 (asdescribed with respect to FIGS. 2I and 4C).

The spaces between the ridges can then be filled with semiconductormaterial in an optional “SEMICONDUCTOR FILL” step 565 and the source anddrain regions for each of the transistors (i.e., the regions not coveredby a gate) can then be doped in a “SOURCE/DRAIN DOPING” step 570 (asdescribed with respect to FIGS. 2J and 4D). Note that in otherembodiments, the source/drain doping performed in step 570 can beperformed before the semiconductor fill operation of step 565. Notefurther that, as described with respect to FIGS. 2I and 2J, step 565 caninvolve etching down the ridges next to some or all of the gates andforming a different semiconductor material over the etched regions(either on individual ridges or as a blanket layer over all ridges) toinduce a desired stress within the channel regions of the devices. Notefurther that in various embodiments, metal-semiconductor compoundformation in source/drain extension regions (and/or source/drainregions) can be performed during step 570 (which can, in certaincircumstances, eliminate the need for doping in the source/drainregions). Finally, any remaining operations for completing the circuitare performed in a “METALLIZATION” step 575 (e.g., source-drain contactregion metal-semiconductor compound formation (e.g., silicidation,germanidation, or germanosilicidation), device passivation (includingany additional stress engineering, such as forming stressed cappinglayers), contact formation, metallization, and PMA, as described withrespect to FIGS. 2K and 4E).

The various embodiments of the structures and methods of this inventionthat are described above are illustrative only of the principles of thisinvention and are not intended to limit the scope of the invention tothe particular embodiments described. Thus, the invention is limitedonly by the following claims and their equivalents.

The invention claimed is:
 1. A semiconductor substrate comprising: aplurality of parallel semiconductor ridges formed on a bulk substrate; aridge insulator material between each of the plurality of parallelsemiconductor ridges, wherein the ridge insulator material is formedbetween sub-surface heavily doped regions of the plurality of parallelsemiconductor ridges; and a plurality of die locations, wherein a firstdepth of sub-surface heavily doped regions of a first plurality ofparallel semiconductor ridges is different than a second depth ofsub-surface heavily doped regions of a second plurality of parallelsemiconductor ridges.